The invention relates to the field of fixators which are used to hold bone parts in a fixed position. Specifically, the present invention is used to hold a hand in a fixed position with respect to the wrist bone and the arm bone when there has been a fracture of the wrist or other wrist disorders.
The fixator is a device which is fixed to the forearm and to the hand by a series of threaded pins inserted into the forearm and hand bones. When such a device is used, there is usually no necessity for a cast. The problem with using existing fixators is that the hand cannot be moved until bone healing takes place. Because the hand is held in a rigid position for a long duration, an extreme stiffness develops in the joint after the fracture has healed. Devices have been developed which permit some movement of the hand under controlled circumstances and prevent this stiffness from developing. These devices, however, have had a very limited range of flexing of the hand with respect to the wrist. Such devices include ball joints which are used on the bar which connects the two sets of pins, and as a result thereof, have a limited range of flexibility.
In an attempt to permit greater movement of the hand with respect to the wrist, various arcuate gears have been developed. Particularly, U.S. Pat. Nos. 2,250,417 to Ettinger, 4,185,623 to Volkov et al., and 4,488,542 to Helland disclose apparatus for setting of bone parts including arcuate gears or guides connecting articulated parts such that the fixator may be shifted along its own axis to provide movement to the limb. The disadvantage with these apparatus is that they do not correspond to the physiologic path of flexion or extension of the patient fitted with the device.
With the above problems in mind, it is desirable to provide a fixator used to hold a wrist in a fixed position with respect to the wrist bone and forearm bones when there has been a fracture of the wrist or other wrist disorder yet allowing some movement of the wrist under controlled circumstances and preventing stiffness in the joint from developing.
It is further been found desirable to provide a fixator used to hold a wrist in a fixed position which includes a compound curve gear adapted to move the wrist through a predetermined path of flexion or extension.
It has further been found desirable to provide a fixator used to hold a wrist in a fixed position which includes a compound curve gear having a plurality of sections each of predetermined varying radius of curvatures which correspond to the physiologic path of flexion or extension of the patient fitted with the device.
The present invention is directed towards solving these problems and provides a workable and economic solution to them.